A HAT-sensitive, non-immunoglobulin secreting human myeloma cell line will be developed and characterized for specific application to human hybridoma production and a low serum or serum-free culture medium will be developed to support the growth of this cell line. NCI's Division of Cancer Biology and Diagnosis in the Omnibus Solicitation recognizes the need of human cell-derived monoclonal antibodies for cancer diagnosis and therapy. During Phase I HAT-sensitive mutants will be developed and characterized from mutated cells originating from the K737 (Lozzio) line which was derived from the pleural effusion of a patient with multiple myeloma. These cells have been treated and survived treatment with either 20 micrograms/ml of 8-azaguanine or 6-thioguanine. They will be cloned in the presence of the mutagen and screened for HAT sensitivity. Positive clones will be further characterized as to growth properties, morphology, fusion efficiency, and immunoglobulin secretion or synthesis. Immunoglobulin levels and growth characteristics will be tested by the PI while karyology studies will be done by Dr. Lozzio. The medium, when developed, will be tested with other cell lines with particular emphasis on supporting the growth of hybridomas of human or mouse origin for the production of monoclonal antibodies in culture without interference of fetal bovine serum proteins. During Phase II the HAT-sensitive HPRT mutants selected from Phase I will be further characterized as to antibody production. (3)